Short-term reactogenicity and gender effect of anthrax vaccine: analysis of a 1967–1972 study and review of the 1955–2005 medical literature

Purpose In the 1960s, the Centers for Disease Control and Prevention (CDC) held the investigational new drug (IND) application for the anthrax vaccine and collected short‐term safety data from approximately 16 000 doses administered to almost 7000 individuals. While some recent anthrax vaccine safety studies have suggested that women experience more injection site reactions (ISRs), to our knowledge the IND safety data were not previously examined for a gender‐specific difference. Methods We identified and analyzed a subset of the IND study data representing a total of 1749 persons who received 3592 doses from 1967 to 1972. Original data collection forms were located and information extracted, including: vaccine recipient's name, age at vaccination, gender, dose number, date of vaccination, lot number, grading of ISR, presence and type of systemic reactions. Overall and gender‐specific rates for adverse reactions to anthrax vaccine were calculated and we performed a multivariable analysis. Results We found an ISR was associated with 28% of anthrax vaccine doses; however, 87% of these were considered mild. Systemic reactions were uncommon (<1%) and most (70%) accompanied an ISR. Our dose‐specific analysis by gender found women had at least twice the risk of having a vaccine reaction compared to men. Our age‐adjusted relative risk for ISR in women compared to men was 2.78 (95%CI: 2.29, 3.38). Conclusions Our results for both overall and gender‐specific reactogenicity are consistent with other anthrax safety studies. To date, possible implications of these gender differences observed for anthrax and other vaccines are unknown and deserve further study.